Lead-free piezoceramics, particularly potassium sodium niobate (KNN)-based compositions, have long been plagued by performance instability and mechanistic ambiguity arising from high processing sensitivity. Here, we develop a robust processing route integrating sand milling, hot pressing and controlled grain coarsening to enable microstructure tuning, improve electromechanical performance, and elucidate grainsize-dependent behavior. Three composition-identical, dense ceramics with distinct grain sizes (0.22, 0.52, and 35.7 & micro;m) are successfully prepared with a 160-fold grain-size difference while maintaining homogeneous microstructures and decent temperature stability. While the fine-grained specimen delivers a piezoelectric coefficient d*33 = 265 pm V-1 together with an excellent Young's modulus Es = 179 GPa and hardness H = 8.71 GPa, the intermediate-grained specimen exhibits the highest piezoelectric response with d*33 = 490 pm V-1 , and the coarse-grained specimen ( similar to 35.7 & micro;m) provides a comparative reference for understanding grain-size effects while maintaining adequate electromechanical properties. These results reveal a non-monotonic dependence of performance on grain size, with an optimum in the submicron regime. By enabling access to multiple grain-size states while preserving microstructural homogeneity, this strategy helps improve performance reliability and guides application-oriented microstructure design in lead-free ceramics. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Complex lead-based perovskites with the general formula Pb(Bx’B1-x’’)O3, represent an important class of antiferroelectrics beyond the prototypical PbZrO3 and NaNbO3. Depending on the combination of B-site species and the degree of cationic ordering, these materials exhibit a wide range of ferroic behaviors, spanning from antiferroelectric to (relaxor) ferroelectric responses. In this study, we investigate (Pb1-xBax)(Yb1/2Nb1/2)O3 polycrystals synthesized via a two-step processing route. Despite displaying antiferroelectric, ferroelectric, or nearly linear dielectric behavior at room temperature, all compositions exhibit double polarization hysteresis loops in proximity to a lower-temperature dielectric anomaly. This dielectric anomaly originates from the competition between antipolar and nanoscale polar regions, and shifts towards lower temperature with increasing Ba content, reflecting the suppression of long-range antiferroelectric ordering. Notably, a composition-invariant temperature scale, T*, is identified and associated with the onset of static correlations among nanoscale polar entities, consistent with behavior reported in other complex Pb-based relaxor ferroelectrics. Superlattice reflections arising from antiparallel Pb2+ displacements persist above T*, suggesting an intricate cation-ordering landscape requiring further investigation. These findings underscore the coexistence and competition of polar and antipolar instabilities in complex lead-based perovskites, and their pronounced sensitivity to chemical substitution, thermal fluctuations, and external electric fields.

Tactile endoscopes can provide physicians with rich sensory information, enabling fast and accurate medical diagnoses. However, existing tactile endoscopy sensors do not consider temperature perception, which is a very important diagnostic indicator in medicine. Here, we report for the first time a tellurium-based superelastic thermoelectric visual-tactile sensor. This platform achieves a breakthrough by combining tellurium thermocouples designed based on crystal structures with viscoelastic silicone encapsulation, enabling simultaneous microscale visual, thermal, and force measurements in a single device. By employing a morphologically optimized tellurium-polymer heterointerface and advanced deep neural network algorithms, we address the inherent trade-off between transparency and responsiveness, achieving artifact-free imaging, real-time thermal mapping, and microstructure force feedback. We conduct clinical endoscopic palpation experiments on live rabbits and successfully achieve tactile diagnosis of inflamed tissue including temperature distribution, especially in cases where visual distinction is difficult, pointing out possible development directions for intelligent endoscopy systems.

Highly effective piezoelectric hardening is crucial for high-power device applications. In this work, we introduce a novel piezoelectric hardening approach that synergistically combines oxygen vacancies with precipitates for achieving strong pinning of ferroelectric domain walls. In Mn-doped 0.2Pb(Zn1/3Nb2/3)O3-0.8Pb(Zr0.5Ti0.5)O3 (Mn-doped PZN-PZT) ceramic, the substitution of Mn3 + for Ti4+ or Zr4+ results in an acceptor doping hardening, whereas the substitution of Mn2+ for Zn2+ leads to the formation of ZnO precipitates, leading to a precipitation hardening. Highly effective piezoelectric hardening via oxygen vacancies and ZnO precipitates in 0.9 wt% MnCO3-doped PZN-PZT sample is realized, where the mechanical quality factor (Qm) and maximum vibration velocity (vmax) represent 10 times and 1.2 times increase, compared to the undoped samples. Moreover, the synergistic strategy of integrating oxygen vacancies with ZnO precipitates can significantly enhance the stability of Qm, offering substantial potential for the design of high-power piezoelectric ceramics.

Ceramic capacitors are critical components in advanced electronic devices, primarily due to their multi-functionalities in energy/information storage and conversion. However, poor temperature stability remains a long-standing challenge for practical applications, especially at extremely high- or low-temperature conditions (e.g., > 200 degrees C or < -55 degrees C). In this work, we propose to combine the advantages of paraelectric Ba0.3Sr0.7TiO3 (BST) with low Curie temperature and relaxor ferroelectric Bi0.325Na0.325Ba0.105Sr0.245TiO3 (BNBST) with high dielectric constant using the spark plasma sintering (SPS) method, aiming to achieve a high and relatively stable dielectric constant over a wide temperature range. The BNBST-0.6BST ceramics exhibit excellent dielectric properties: an ultrahigh dielectric constant of 3912 with the change of less than +/- 15% over an ultrawide temperature range from -90 degrees C to 400 degrees C, significantly exceeding the standard of X9R. Additionally, the BNBST-0.6BST ceramics also achieve a recoverable energy storage density of 3.5 J cm(-3) under a moderate electric field of 270 kV cm(-1), with excellent stability and reliability. This work demonstrates the potential application of high dielectric constant BNT-based ceramics over an ultrawide temperature range, driving the development of ceramic capacitors in extremely harsh service environments.

Vibrating mesh nebulizers (VMNs) have been extensively used as household medical devices. However, lead-free VMNs have rarely been reported since their invention. Herein, we present a (K,Na)NbO3-based (KNN) lead-free piezoceramic with comparable electrical properties to those of conventional lead-containing counterparts, and for the first time, develop an environmentally benign VMN. The KNN-based piezoceramic demonstrates better electric-field-induced strain (Delta S = 0.23 %) and normalized strain (d33* = 437 p.m./V) compared to lead zirconate titanate (PZT), which is commercially employed in VMNs. Both theoretical finite element analysis (FEA) and experimental 3D laser Doppler vibrometry confirm that the KNN-based piezoceramic component exhibits larger center displacement than PZT. Furthermore, the KNN-based nebulizer generates finer aerosol droplets 3.33 +/- 0.04 mu m when using water as a substitute for medical fluids. This breakthrough not only highlights the potential of KNN-based materials as a sustainable alternative to lead-based piezoelectric but also paves the way for the development of eco-friendly medical devices.

Potassium sodium niobate (KNN) has emerged as a promising lead-free piezoelectric material owing to its competitive piezoelectric performance and environmental compatibility; however, its relatively poor dielectric properties limit high-power applications and long-term reliability. Here, the electrical conductivity of doped KNN is investigated using density functional theory in conjunction with the Kubo-Greenwood formalism. Pristine KNN is confirmed to exhibit very low electrical conductivity, in good agreement with experimental measurements, supporting the validity of the present computational approach, while the introduction of intrinsic and extrinsic defects can significantly modify its electronic structure and transport behavior. The present calculations provide a clear electronic-structure-based explanation for the previously reported results showing that Fe doping enhances carrier mobility, whereas Ca doping has only a minor influence on the electronic structure and electrical conductivity. In contrast to common assumptions, although the impact of Mn doping on the electronic structure depends strongly on its valence state, Mn incorporation generally leads to an enhancement of electrical conductivity in KNN. The resulting performance improvement of Mn-doped KNN therefore reflects a balance between increased electrical conductivity and the suppression of oxygen-vacancy-related defects. Overall, these results provide a microscopic understanding of how defects regulate the electrical conductivity of lead-free piezoelectric oxides.

Amorphous potassium sodium niobate (KNN) thin films were deposited onto Pt/Ti/SiO2/Si substrates at 200°C using magnetron sputtering. The resultant films were then annealed in an alkali metal element atmosphere formed by alkali metal carbonates. The influence of annealing dwell time on the films' properties was investigated. It was observed that while the overall crystalline phase and elemental composition of the films remained essentially unchanged, their electrical characteristics exhibited systematic variations. Microscopic analysis revealed that extending the annealing time within an optimal range facilitated the formation of ferroelectric domain structures and enhanced piezoresponse phase contrast between domains. However, prolonged annealing led to localized phase segregation, resulting in performance degradation. Our results provide useful insights into the fabrication of KNN thin films using magnetron sputtering or other thermally involved synthesis methods.

The prominent electromechanical conversion properties of piezoelectric materials render them extensively employed in high-power and high frequency devices. With the environmental friendliness, potassium sodium niobate (KNN)-based lead-free ceramics have gained significant attention because of their outstanding piezoelectric performance and high Curie temperature (TC). But the unbalanced development between piezoelectric constant (d33) and mechanical quality factors (Qm) is an obstacle to their applications. In this work, the influence of K/Na ratio-induced defect structure on the comprehensive properties are discussed of KNN-based lead-free ceramics. Phase transition from orthorhombic-tetragonal (O-T) to rhombohedral-orthorhombic-tetragonal (R-O-T) is observed during increasing K+, along with refined domain structure. Significantly, A-site vacancy increases as well as decreased oxygen vacancy due to stronger volatility of K with respect to that of Na, which reduces the defect dipoles and weakens the pinning effect. Then, Qm decreases with increasing K/Na ratio, while the d33 is improved because of not only multiphase coexistence but also an elevated A-site vacancy which can facilitate domain switching with lowered polarization anisotropy and energy barrier. This work further analyzes the effect of defect structures on the properties of KNN-based ceramics, providing a specific strategy to gain high-performance lead-free ceramics for high-power applications.

Present main-stream medical ultrasonic nebulizers contain Pb(Zr,Ti)O3-based piezoceramics, which could expose the patients to toxic lead when the acidic liquid medicine, compounded with ultrasonic vibration, corrodes the piezoceramics. Enormous amount of lead ions up to 150 ppm can be extracted when lead-containing piezoceramics were exposed to typical acidic liquid medicines. Thus, a series of nebulization in a course of treatment could easily raise a child's blood lead level well above the blood lead reference value of 0.035 ppm, causing adverse and likely irreversible health effects. Herein, we introduce the lead-free medical ultrasonic nebulizers based on high-performance (K,Na)NbO3-based lead-free piezoceramics. It's designed for facile and safe at-home treatment, offering a healthy, safe, and lead-free solution for patients. It also marks the first commercialization of (K,Na)NbO3-based lead-free piezoceramics as a replacement for Pb(Zr,Ti)O3, helping expedite the lead-removing process of piezoelectric materials in general, in line with sustainable development goals worldwide.

Pb(Zr,Ti)O3 (PZT) ceramics play a crucial role in fields such as national defense, healthcare, communication, and energy conversion due to their excellent piezoelectric, ferroelectric, and pyroelectric properties. However, the sintering temperature of PZT ceramics usually exceeds 1200 degrees C, resulting in high energy consumption and a large amount of PbO volatilization. This volatilization disrupts the stoichiometric balance of PZT ceramics, thereby adversely affecting their electrical properties. Moreover, the rapid development of piezoelectric multilayer devices further requires PZT ceramics to be co-sintered with low-cost metal electrodes at low temperatures. To address these challenges, researchers have extensively investigated the low-temperature sintering of PZT piezoelectric ceramics, successfully reducing the sintering temperature of PZT ceramics to below 1000 degrees C, which has attracted widespread attention. Starting from the structural characteristics and physical properties of PZT ceramics, this article reviews the current research status of low-temperature sintering technology in the field of PZT ceramics. It mainly introduces the current status of low-temperature sintering techniques, including spark plasma sintering, hot-pressing sintering, cold sintering, as well as the use of sintering aids such as forming solid solutions, liquid-phase sintering, and transient liquid-phase sintering. The influence of these sintering techniques on the microstructure and electrical properties of PZT piezoelectric ceramics is systematically summarized. The issue of electrical performance degradation caused by sintering aids and possible solutions are analyzed. At last, future development trends of low-temperature sintering technologies for PZT ceramic are explored.

Lead-free potassium sodium niobate [(K0.5Na0.5)NbO3, KNN]-based piezoceramics have emerged as promising alternatives to lead-based counterparts. Although grain-size effects in KNN ceramics have been widely investigated, most prior studies relied on doping strategies, introducing additional variables that complicate interpretation. The intrinsic microscopic mechanisms of their grain size effects remain inadequately understood. In this work, the influence of grain size on domain structures and ferroelectric properties was systematically investigated in pure KNN ceramics with controlled uniform grain sizes (similar to 0.5, similar to 3, and similar to 9 mu m). Comprehensive characterization combining piezoresponse force microscopy and macroscopic ferroelectric measurements reveals that although saturated polarization is similar across different grain sizes, polarization switching responses to applied electric fields vary substantially. Small grains predominantly exhibit simplified 180 degrees domain configurations resulting from elevated grain-boundary-induced residual stresses, leading to higher coercive fields and reduced domain growth dynamics (growth rate, similar to 169 nm(2) V-1). Conversely, large grains feature diverse non-180 degrees domains, which facilitate polarization switching at lower electric fields with an enhanced domain growth of similar to 270 000 nm(2) V-1. These results demonstrate that different grain boundary densities critically affect internal stress distributions and domain structures, thereby determining domain switching kinetics and macroscopic electromechanical performances. This study provides essential insights into the microscopic mechanisms underlying grain size effects in lead-free piezoelectric ceramics.

Piezoelectric materials are indispensable in electromechanical actuators, which require a large electrostrain with a fast and precise response. By designing a chemopiezoelectric effect, we developed an approach to achieve a high electrostrain of 1.9% under -3 kV mm-1, at 1 Hz, corresponding to an effective piezoelectric coefficient of >6,300 pm V-1 at room temperature in lead-free potassium sodium niobate piezoceramics. This electrostrain has satisfactory fatigue resistance and thermal stability, and low hysteresis, far outperforming existing lead-based and lead-free perovskite counterparts. From tracer diffusion, atomic optical emission spectrometry experiments, combined with machine-learning molecular dynamics and phase-field simulations, we attribute the high electrostrain to short-range hopping of oxygen vacancies near ceramic surfaces under an alternating electric field, which is supported by strain levels reaching 3.0% under the same applied field when the sample was annealed at a low oxygen partial pressure. These findings provide an additional degree of freedom for designing materials on the basis of defect engineering, which will favour not only the electrostrain of piezoelectrics but also the functional properties of a broader range of oxide-based materials.

With the rapid expansion of the Internet of Things, piezoelectric energy harvesting has become essential for sustainable self-powered microsystems. However, achieving sufficient output current under operating conditions remains a persistent challenge. Herein, a phase-boundary and bandgap co-engineering strategy is implemented for potassium sodium niobate-based ceramics by incorporating BiFeO3 into 0.97(K0.5Na0.5)(Nb0.96Sb0.04)O3-0.03(Bi0.5Na0.5)0.85(Li0.5Nd0.5)0.15ZrO3. This induces a rhombohedral-tetragonal phase boundary that establishes nanoscale multiphase coexistence alongside an elevated average polarization displacement, enabling an exceptional piezoelectric coefficient. Simultaneously, ultralow resistivity is achieved through the lower bandgap resulting from BiFeO3 incorporation. This design achieves ultrahigh current density (50 μA/cm2) and power density (860 μW/cm3). Atomic-resolution structural analyses reveal that continuous rotation of the polarization vector, promoted by multi-directional polar states and high-density multiscale nanodomains, suppresses polarization anisotropy and domain-wall pinning, thereby synergistically amplifying piezoelectric responses. Concurrently, narrow-bandgap BiFeO3 doping elevates oxygen-vacancy concentration, lowering the conduction-band minimum and narrowing the bandgap, further reducing resistivity. The authors propose a phase-boundary and bandgap co-engineering strategy by incorporating BiFeO3 into 0.97(K0.5Na0.5)(Nb0.96Sb0.04)O3-0.03(Bi0.5Na0.5)0.85(Li0.5Nd0.5)0.15ZrO3, greatly improving the output current performance.

Piezoelectric ultrasonic motors play a pivotal role in advancing intelligent and high-tech applications, drawing significant attention to the study of defects in piezoelectric materials. Defect modulation, achieved through the incorporation of appropriate additives, stands out as a proven and effective strategy for enhancing the performance of ceramics. Herein, defect structure and the orientation behavior under external fields has been emphasized on in potassium sodium niobate ceramics with excess bismuth. Elevated defect polarization is revealed with increased A-site vacancy and decreased oxygen vacancy when bismuth is strongly excessive, along with lowered orthorhombic-tetragonal phase transition temperature. The defect polarization is oriented under a high electric field and depolarized under a strong thermal field. This is evidenced by asymmetric ferroelectric hysteresis loops and a large internal bias field in poled ceramics, while unpoled and depolarized samples display nearly symmetrical loops. Additionally, asymmetric bipolar strain curves with a notable deviation between positive and negative electric fields are observed in poled samples, whereas annealing reduces this asymmetry. Meanwhile, the domain switching becomes more difficult in the poled state compared to the virgin state due to the pinning effect induced by oriented defect polarization during pre-poling. Then, large Qm and d33 as well as decreasing and increasing tendencies respectively, are gained simultaneously with increased defect, generated by the strong promoted domain switching from elevated A-site vacancy and lowered phase transition temperature, with respect to the impeded effect from pinning effect of defect dipoles. Therefore, this study demonstrated the defect evolution under external fields and the impact on macro-performance, accelerating the material development for piezoelectric motors.

Currently, achieving highly symmetrical bipolar strain and high electrostrain under low driving electric field remains challenging in piezoelectric materials. The designed potassium sodium niobate-based ceramics exhibit highly symmetrical bipolar strain and ultrahigh electrostrain coefficient (~2000 pm/V) under a low driving electric field of 8.4 kV/cm through A-site defect engineering and charge compensation. The highly symmetrical bipolar strain is related strongly to the lowly aligned defect dipoles by partially substituting A-site (Na+/K+) ions with Mn2+. The eye-catching performance is ascribed to the unique microstructure of atomic-scale polar nanoregions embedded in nano-domains (~34 nm) by tuning Na+/K+ ions deficiency and coexistence of multiple phases. Phase-field simulations reveal that flattened energy barrier and multiphase nanodomains interplay to boost electrostrain at low driving fields. This work provides an innovative way of designing lead-free piezoelectric materials with highly symmetrical bipolar strain and giant electrostrain coefficient at low driving electric field, promising for high-precision actuators applications.

Dielectric capacitors are independent in advanced electronics and pulse power systems as an energy storage and conversion medium. However, achieving high energy density at a low electric field remains challenging for dielectric materials to improve the safety of integrated electronic devices. In this work, the strategy of defect engineering-induced phase competition is proposed to improve the polarization behavior and strengthen dielectric temperature stability of (Bi,Na)TiO3 (BNT)-based relaxor ferroelectric, i.e., Na0.325Sr0.245Ba0.105–1.5x□0.5xBi0.325+xTiO3 (NSB0.105–1.5x□0.5xB0.325+xT) ceramics by changing the ratio of Bi3+/Ba2+. A high recoverable energy density (Wrec=3.6 J/cm3) is achieved at a relatively low electric field of 160 kV/cm for x=0.06 composition together with a high dielectric constant of 3142±15% in a wide temperature range of 30–386 °C, which exceeds other lead-free dielectric ceramics at the same electric field. The results demonstrate that NSB0.015□0.03B0.385T ceramics are desirable for advanced pulsed power capacitors and will push the development of defect-tuned functionality of dielectric ceramics for energy storage applications.

Densification of faceted grain ceramics, exemplified by lead-free piezoelectric potassium sodium niobate (KNN), remains a longstanding challenge due to preferential grain growth and directional diffusion, which degrade performance and hinder practical applications. Here, chemical modification via single-element Ti doping enables high densification (98% relative density) with submicron grains (0.36 mu m) in KNN ceramics. Substitution of Ti4+ at Nb5+ sites generates both oxygen vacancies and substitutional defects, which reshape the energy landscape by elevating crystallographic plane interfacial energy while suppressing step free energy. This strategy redirects sintering driving forces toward densification over grain growth, enabling fine-grain densification. This work develops a disorder-mediated framework-integrating defect chemistry, interfacial energy anisotropy, and grain growth kinetics-to decipher densification mechanisms of faceted grain ceramics. The approach not only deepens fundamental insights but also provides a scalable method to manufacture high-quality faceted grain ceramics for industrial processing.